@media (max-width: 960px) {
    main > *:nth-child(1) {
        background-color: red;
    }
    main > *:nth-child(2) {
        background-color: green;
    }
    main > *:nth-child(3) {
        background-color: blue;
    }
}

@media (max-width: 768px) {
    sidebar:first-child {
        width: 50%;
    }
    sidebar:last-child {
        width: 100%;
    }
}

@media (max-width: 540px) {
    sidebar:first-child {
        width: 100%;
    }
}

@media (max-width: 480px) {
    .content {
        order: -1;
    }
}